The invention relates to broad-band, passive ring mixers, particularly those used as input mixers in meters or decimeter wave receivers.
Diode ring modulators and in particular those having a ring with four identical diodes are known to have good characteristics at high frequencies and in particular their circuits have a low impedance permitting a wide pass band. However, the satisfactory performances in intermodulation and transmodulation are dependent on an adequate local oscillating power.
At high frequencies, for example in the decimeter wave band, the overall efficiency of a local oscillator is low, approximately 10 to 15%, and portable and self-contained receivers suffer a considerable reduction in their operating autonomy due to their energy consumption needs for obtaining this adequate power.
Numerous ring mixer constructions are known, which use active transformers in place of diodes in order to improve their gain. They make it possible to reduce the local oscillating power, but the sought highly satisfactory linearity conditions are not obtained in any of these constructions due to the intrinsic defects of the active transistors, particularly the exponential characteristics of the base current as a function of the base-emitter voltage and the variations in the current amplification factor with that of the collector current. There are also balancing difficulties due to the dispersion of the characteristics.